Ultraviolet light has a degradative effect on olefin polymers, the severity of which is dependent on the particular polymer and the geographical location of exposure. The degradation may take the form of discoloration, loss of tensile and impact strength, distortion of initial flexibility, dimensional change, surface craze, cracking, powdering or increased electrical conductivity. All of these effects may result from the breaking of carbon-to-carbon bonds in the polymer chain followed by immediate oxidation of the chain fragments.
It is well known that the addition of certain materials to an olefin polymer will impart a degree of stabilization to that polymer with respect to its resistance to the destructive forces of ultraviolet radiation. These materials, in one instance, function as preferential acceptors of incident ultraviolet radiation because they have a much higher affinity for such radiation than does the olefin polymer. It appears that they absorb harmful radiation and dissipate it as harmless energy. They thus form a protective shield for the polymer in which they are present.
Although there are many types of ultraviolet stabilizers, an important class includes the 2-hydroxyphenylbenzotriazoles. They offer strong intensity and broad ultraviolet stabilization with a fairly sharp wavelength limit close to the visible region. They absorb light at 280-390 mm.
Olefin polymers which are stabilized by an ultraviolet stabilizer frequently contain also an oxidation inhibitor. This is especially so where it is important to achieve light stable polymer compositions. A wide variety of antioxidants are available.
McNally, U.S. Pat. No. 4,000,101, teaches the combined use of certain phenolic antioxidants, pentaerythritol diphosphites and ultraviolet stabilizers, in olefin polymers. The compositions there disclosed, however, contain a rather complex polythiopolyphoshite as the principal polymer additive.
Mills, U.S. Pat. No. 3,988,293, shows the particular combination of 2-hydroxy-4-n-octoxybenzophenone and distearyl pentaerythritol diphosphite as a stabilizer for olefin polymers.
The specification of pending U.S. application Ser. No. 697,637, filed June 18, 1976, teaches the combination of distearyl pentaerythritol diphosphite with a wide variety of other polymer additives including 2,(2'-hydroxy-5'-methyl phenol)benzotriazoles.
Dexter et al., U.S. Pat. No. 3,285,855 and U.S. Pat. No. 3,644,482, show (4-hydroxy-5-alkylphenyl)alkanoic acid esters of monohydric and polyhydric alcohols and refer to their combined use with "synergizing stabilizers (UV absorbers, phosphites, dialkyl thiodipropionates, and the like." Gilles, U.S. Pat. No. 3,531,483 contains a similar statement, applicable to the hydroxyphenylalkeneyl isocyanurates.